Increasingly a main attraction of CNN, MSNBC and Fox News, the interactive screens, loaded with data and visual effects, bring a sci-fi gloss to cable news and transform granular data into something viewers can actually see.

Pioneered by CNN a decade ago, the screens have also made stars of their human minders, the anchors who blend wonk-level knowledge with tap-and-swipe dexterity. Fleet fingers, and a mind for numbers, are essential.

We spoke with three anchors known for their map skills about how they are preparing for Tuesday night, when they will report on the decisions by voters in nearly 500 House and Senate races.

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“It’s a breathtaking tool for me,” John King of CNN says of the network's "Magic Wall." “It teaches you about America.”CreditT.J. Kirkpatrick for The New York Times

CNN

John King

They call it the “Magic Wall.” And like the typical celebrity, it seems smaller when you see it in person.

The CNN map is housed in a chrome casing on the 11th floor of the cable network’s Washington studio. Mr. King has worked the map since its debut in 2008, and a few days before the midterm elections, he greeted it like an old friend.

“It’s a breathtaking tool for me,” Mr. King said as he caressed the screen, scrolling past graphics and menus. “It teaches you about America.”

During the 2016 election, as the nation tipped Trumpward, CNN’s cameras stayed glued to the map as Mr. King laid out in clinical detail exactly why the numbers in Florida and Michigan were not adding up for Hillary Clinton. Even President Trump, no CNN loyalist, was watching from Trump Tower.

“John King, nice guy!” Mr. Trump told supporters at a rally a few weeks after his victory. “He’s got the map — he’s good with the map! — but his hand is starting to shake.”

The anchor said he later watched the tape of his election-night performance to check: “My hands weren’t shaking,” he said.

In his years with the map, Mr. King, 55, has developed a few rules of thumb.

First, use the appropriate finger. There was the time he pointed out a precinct with the digit between pointer and ring. “I was flipping the country the bird,” he recalled. “So you learn.”

Mr. King is left-handed, but he has trained his right hand to take care of the heavy-duty scrolling and zooming. And if he has to turn his body away from the camera, he makes sure to say “excuse me” to viewers.

“I think it’s weird on television, if you’re turning your back on somebody,” he said.

Mr. King says he works out on Election Day mornings, and he is careful to stretch his hands and wrists ahead of showtime. Washing his hands is also important, to avoid smudging the screen’s surface. How about a manicure? “I clip my own nails,” Mr. King said. “I’m a kid from Dorchester, Mass. I don’t think I’ll ever get a manicure.”

The 2018 map, he said, has sharper colors and more computing power than previous versions. “Think about your phone 10 years ago and your phone today,” he said.

The Magic Wall technology was designed for military use, in situation rooms of the C.I.A., not CNN, variety. A producer spotted it at a trade show and decided the network could take advantage.

During breaks, Mr. King retreats to a hidden nook near the map for water and espresso. “Wolf keeps a flask of whiskey,” Mr. King joked, referring to his CNN colleague Wolf Blitzer. “He’s actually a robot. We keep that from the world.”

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“The lesson I take from TV is the less rehearsed it is, the more natural it’s going to seem,” said Steve Kornacki, the MSNBC map operator. “Don’t overthink it. It seems to work enough for me, and I’ll just keep doing it.”CreditJeenah Moon for The New York Times

MSNBC

Steve Kornacki

Mr. Kornacki at the map is something to behold.

MSNBC’s map correspondent jabs at various counties. He waves his arms like a third base coach. He doesn’t so much swipe the screen as manhandle it.

During the Pennsylvania special election this year, Mr. Kornacki, live on the air and ready to speak, seemed flummoxed by a pen that was lodged in his mouth. Instead of pulling it out with his fingers, he spat it to the floor.

“When people showed it to me, I said, ‘Ugh, I did that?’” Mr. Kornacki said of the pen moment.

MSNBC considers Mr. Kornacki’s unpolished presence a plus. The network has even shown a commercial that captures him in mad-professor mode as the anchor Brian Williams says, “If you saw the movie ‘A Beautiful Mind,’ then the Steve Kornacki portion of your picture will look familiar to you.”

“The lesson I take from TV is the less rehearsed it is, the more natural it’s going to seem,” Mr. Kornacki said. “Don’t overthink it. It seems to work enough for me, and I’ll just keep doing it.”

He is also making a mark on pop culture. On a recent episode of “Murphy Brown,” the title character tells a young social media manager working the map on an election night special that he was channeling “his inner Kornacki.”

At a rehearsal at 30 Rockefeller Plaza days before the midterms, the real Mr. Kornacki, 39, was working with a newly juiced-up model of the board that can zoom in on the most obscure House districts.

Watching Mr. Kornacki was David Bohrman, a longtime election-coverage producer now consulting with MSNBC, who noted that the map had made it easier to cover races that once received little airtime.

“The House has always been a package at the end of the night,” Mr. Bohrman said. “Now we have the display technology that Steve can drive to illustrate it and explain it.”

Mr. Kornacki will feel emboldened to geek out on Tuesday, he said, because his audience is more sophisticated than it was when he started as MSNBC’s map man four years ago.

“They have gotten smarter with this stuff,” he said. “Online, the literacy about target districts and things like this, there’s this culture that has developed around it. I’ve had conversations with people in the last two years that I would not have had five years ago.”

And all that energy? That’s because standing beside the map is exactly where he wants to be.

“I got here in 2012, and my boss Phil Griffin called me up in 2014 and said, ‘We’ll give you a shot on the board,’” he said, referring to the MSNBC president. “And I said, ‘Thank you!’ This is the thing that I really kind of wanted to do here. I think maybe that energy or whatever — maybe it’s too much — I think that’s probably what that is.”

Mr. Hemmer, a co-anchor of the midmorning Fox News show “America’s Newsroom,” has been in charge of the map since the 2008 primary season.

“I like numbers. And I like geography. And I like politics,” he said.

But even a veteran like Mr. Hemmer seems blown away by the latest model.

“In 2014, the midterm race was all about the Senate,” he said, standing inside the Fox News studio in Midtown Manhattan. “That’s where the story was, and it was an easy thing to touch a screen and turn a state from blue to red, or red to blue. This is so much more complex.”

Mr. Hemmer demonstrated the latest widgets. A simple click allowed him to zoom his way from a Colorado battleground to a key New Jersey county. And he can now project data points onto a giant screen nearby, which allows him to roam the studio, untethered from the Bill Board.

“It’s like going from an iPhone 6 to the iPhone X,” Mr. Hemmer said.

Of all the map men, Mr. Hemmer seems the most sartorially conscious. Zegna suit. Bruno Magli shoes. Tapping a sole of his shoes, he said, “These are great for studio work because they have soft bottoms.”

Will he go with the natty pocket square he wore during his coverage of the 2016 election?

Game-time decision, Mr. Hemmer said.

Michael M. Grynbaum is a media correspondent covering the intersection of business, culture and politics. @grynbaum

John Koblin covers the television industry. He reports on the companies and personalities behind the scripted TV boom, and the networks that broadcast the news. He previously covered fashion. @koblin

A version of this article appears in print on , on Page A19 of the New York edition with the headline: They’ve Got the Touch: The Cable Networks’ Election Night Map Men. Order Reprints | Today’s Paper | Subscribe